Abstract
A new coumarin derivative containing benzothiazole and piperazine substituents was synthesized. Preferential inclusion of the benzothiazole group, over the coumarin and piperazine groups, inside the cavity of the molecular container cucurbit[7]uril (CB7) was evidenced by using optical and NMR techniques. The binding constant of the new complex with CB7 is higher in its protonated forms (e.g., K=2.8×106M−1) than in its neutral forms, which led to an increase in the pKa value associated with protonation of the aza nitrogen on the benzothiazole ring of ca. 2.5units. Such CB7-induced protonation disabled the photoinduced electron transfer (PET) in the included molecule, enhancing its coumarin fluorescence up to ca. 45-fold (pH 3.5, 410nm). The results are discussed in the context of designing sensitive analytical tools for reversible monitoring of optically inactive analytes by competitive displacement experiments.
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